Relay Link HARQ Operation

ABSTRACT

A method for preventing a first network node from missing a transmission from an second network node. The method includes, when a ten millisecond periodicity is used for Multicast/Broadcast Single Frequency Network (MBSFN) subframes, setting a time between an uplink grant from the second network node to the first network node and an acknowledgement/negative-acknowledgement message (ACK/NACK) from the second network node to the first network node equal to ten milliseconds. The method further includes, when a forty millisecond periodicity is used for MBSFN subframes, the second network node sending the first network node an asynchronous grant for an uplink retransmission when a data packet is missed, and when the first network node receives the grant for the uplink retransmission, the first network node retransmitting the missed data packet.

BACKGROUND

As used herein, the terms “user agent” and “UA” might in some casesrefer to mobile devices such as mobile telephones, personal digitalassistants, handheld or laptop computers, and similar devices that havetelecommunications capabilities. Such a UA might consist of a device andits associated removable memory module, such as but not limited to aUniversal Integrated Circuit Card (UICC) that includes a SubscriberIdentity Module (SIM) application, a Universal Subscriber IdentityModule (USIM) application, or a Removable User Identity Module (R-UIM)application. Alternatively, such a UA might consist of the device itselfwithout such a module. In other cases, the term “UA” might refer todevices that have similar capabilities but that are not transportable,such as desktop computers, set-top boxes, or network appliances. Theterm “UA” can also refer to any hardware or software component that canterminate a communication session for a user. Also, the terms “useragent,” “UA,” “user equipment,” “UE,” “user device” and “user node”might be used synonymously herein.

As telecommunications technology has evolved, more advanced networkaccess equipment has been introduced that can provide services that werenot possible previously. This network access equipment might includesystems and devices that are improvements of the equivalent equipment ina traditional wireless telecommunications system. Such advanced or nextgeneration equipment may be included in evolving wireless communicationsstandards, such as long-term evolution (LTE). For example, an LTE systemmight include an Evolved Universal Terrestrial Radio Access Network(E-UTRAN) node B (eNB), a wireless access point, or a similar componentrather than a traditional base station. As used herein, the term “accessnode” will refer to any component of a wireless telecommunicationssystem, such as a traditional base station, a wireless access point, oran LTE eNB, that creates a geographical area of reception andtransmission coverage allowing a UA or a relay node to access othercomponents in the system. An access node may comprise a plurality ofhardware and software.

The term “access node” does not refer to a relay node, which is acomponent in a wireless network that is configured to extend or enhancethe coverage created by an access node or another relay node. The accessnode and relay node are both radio components that may be present in awireless communications network, and the terms “component” and “networknode” may refer to an access node or relay node. It is understood that acomponent might operate as an access node or a relay node depending onits configuration and placement. However, a component is called a “relaynode” only if it requires the wireless coverage of an access node orother relay node to access other components in a wireless communicationssystem. Additionally, two or more relay nodes may be used serially toextend or enhance coverage created by an access node.

The signals that carry data between UAs, relay nodes, and access nodescan have frequency, time, and coding parameters and othercharacteristics that might be specified by a network node. A connectionbetween any of these elements that has a specific set of suchcharacteristics can be referred to as a resource. The terms “resource,”“communications connection,” “channel,” and “communications link” mightbe used synonymously herein. A network node typically establishes adifferent resource for each UA or other network node with which it iscommunicating at any particular time.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a diagram illustrating a wireless communication system thatincludes a relay node, according to an embodiment of the disclosure.

FIG. 2 is a diagram of a timeline for downlink transmissions to and froma relay node.

FIG. 3 is a diagram of a timeline for downlink transmissions to and froma relay node according an embodiment of the disclosure.

FIG. 4 is an alternative diagram of a timeline for downlinktransmissions to and from a relay node.

FIG. 5 is a diagram of a timeline for downlink transmissions to and froma relay node according an alternative embodiment of the disclosure.

FIG. 6 is a diagram of a timeline for downlink transmissions to and froma relay node according an alternative embodiment of the disclosure.

FIG. 7 is a diagram of a mapping of MBSFN subframes and correspondingACK/NACK subframes according an embodiment of the disclosure.

FIG. 8 is a diagram of multiple timelines depicting the use of a “smart”NACK according to an embodiment of the disclosure.

FIG. 9 is a diagram of multiple timelines depicting a technique foravoiding collisions between uplink transmission from a relay node anduplink transmissions from a UA according to an embodiment of thedisclosure.

FIG. 10 is a diagram of a timeline for downlink transmissions to andfrom a relay node according an alternative embodiment of the disclosure.

FIG. 11 illustrates a processor and related components suitable forimplementing the several embodiments of the present disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents.

FIG. 1 is a diagram illustrating a wireless communication system 100that includes a relay node 102, according to an embodiment of thedisclosure. Examples of the wireless communication system 100 includeLTE or LTE-Advanced (LTE-A) networks, and all of the disclosed andclaimed embodiments could be implemented in an LTE-A network. The relaynode 102 can amplify or repeat a signal received from a UA 110 and causethe modified signal to be received at an access node 106. In someimplementations of a relay node 102, the relay node 102 receives asignal with data from the UA 110 and then generates a new signal totransmit the data to the access node 106. The relay node 102 can alsoreceive data from the access node 106 and deliver the data to the UA110.

The relay node 102 might be placed near the edges of a cell so that theUA 110 can communicate with the relay node 102 rather than communicatingdirectly with the access node 106 for that cell. In radio systems, acell is a geographical area of reception and transmission coverage.Cells can overlap with each other. In the typical example, there is oneaccess node associated with each cell. The size of a cell is determinedby factors such as frequency band, power level, and channel conditions.Relay nodes, such as relay node 102, can be used to enhance coveragewithin a cell or to extend the size of coverage of a cell. Additionally,the use of a relay node 102 can enhance throughput of a signal within acell because the UA 110 can access the relay node 102 at a higher datarate than the UA 110 might use when communicating directly with theaccess node 106 for that cell, thus creating higher spectrum efficiency.The use of a relay node 102 can also decrease the UA's battery usage byallowing the UA 110 to transmit at a lower power.

Relay nodes can be divided into three types: layer one relay nodes,layer two relay nodes, and layer three relay nodes. A layer one relaynode is essentially a repeater that can retransmit a transmissionwithout any modification other than amplification and slight delay. Alayer two relay node can decode a transmission that it receives,re-encode the result of the decoding, and then transmit the re-encodeddata. A layer three relay node can have full radio resource controlcapabilities and can thus function similarly to an access node. Theradio resource control protocols used by a relay node may be the same asthose used by an access node, and the relay node may have a unique cellidentity typically used by an access node. The illustrative embodimentsare primarily concerned with layer two or layer three relay nodes.Therefore, as used herein, the term “relay node” will not refer to layerone relay nodes, unless specifically stated otherwise.

When the UA 110 is communicating with the access node 106 via the relaynode 102, the links that allow wireless communication can be said to beof three distinct types. The communication link between the UA 110 andthe relay node 102 is said to occur over an access link 108. Thecommunication between the relay node 102 and the access node 106 is saidto occur over a relay link 104. Communication that passes directlybetween the UA 110 and the access node 106 without passing through therelay node 102 is said to occur over a direct link 112.

Data is transmitted between the access node 106, the relay node 102, andthe UA 110 in a series of subframes, each typically having a duration of1 millisecond (ms). Ten contiguous subframes comprise one radio frame.Each subframe consists of a relatively shorter control region followedby a relatively longer data region. The control region, or physicaldownlink control channel (PDCCH), typically consists of one to fourorthogonal frequency-division multiplexing (OFDM) symbols. The dataregion, or physical downlink shared channel (PDSCH), can be considerablylonger.

Some subframes contain unicast control data in the PDCCH region andmulticast/broadcast data in the PDSCH region in order to support theMultimedia Broadcast/Multicast service (MBMS). For historical reasons,such subframes are known as Multicast/Broadcast Single Frequency Network(MBSFN) subframes. In a unicast system, if a subframe is configured asan MBSFN subframe, the subframe contains data only in the PDCCH regionand there is no data in the PDSCH region. In a non-MBSFN subframe, datais typically transmitted throughout the duration of the subframe. In anMBSFN subframe, the relay node 102 transmits downlink data only for theduration of the PDCCH region. The relay node 102 then disables itsdownlink transmitter and enables its downlink receiver for the remainderof the subframe. For various technical and expense reasons, the relaynode 102 typically cannot transmit and receive data within the samefrequency band at the same time. Therefore, the relay node 102 cantypically receive data from the access node 106 in an MBSFN subframeonly after the relay node 102 has completed transmitting PDCCH data,disabled its downlink transmitter, and enabled its downlink receiver.

MBSFN subframes can occur in subframes 1, 2, 3, 6, 7, or 8 of a radioframe (with indexing beginning at 0), but will not necessarily occur inall of those subframes. The access node 106 specifies which subframeswill be MBSFN subframes and signals that information to the relay nodesand the UAs. This could be done via higher layer control signaling. Theaccess node 106 transmits data to the relay node 102 only in MBSFNsubframes, so from the perspective of the relay node 102, MBSFNsubframes can be considered reception subframes. Downlink transmissionsfrom the relay node 102 to the UA 110 must occur in subframes 0, 4, 5,and 9 of a radio frame, and may occur in the remaining subframes.Therefore, from the perspective of the relay node 102, subframes 0, 4,5, and 9 can be considered mandatory transmission subframes.

Among the data that the relay node 102 might receive from the accessnode 106 in an MBSFN subframe is an uplink grant informing the relaynode 102 of a resource that the relay node 102 can use to transmit datato the access node 106. When the relay node 102 wishes to send data tothe access node 106, the relay node 102 can send a resource request tothe access node 106. The access node 106 can then, in a downlinktransmission to the relay node 102, allocate a resource to the relaynode 102 that the relay node 102 can use to send its data to the accessnode 106. That is, in an MBSFN subframe, the access node 106 might grantthe relay node 102 the use of a communication channel with a specificset of frequency parameters and other characteristics that the relaynode 102 can use on an uplink to the access node 106. In a similar way,the relay node 102 can grant an uplink resource to the UA 110 that theUA 110 can use to send data to the relay node 102.

Hybrid Automatic Repeat Request (HARQ) is an error control method thatmight be used in data transmissions between the access node 106, therelay node 102, and the UA 110. In HARQ, additional error detection andcorrection bits are added to a data transmission. If the recipient ofthe transmission is able to successfully decode the transmitted bits,then the recipient accepts the data block associated with the encodedbits. If the recipient is not able to decode the transmitted bits, therecipient might request a retransmission. For example, upon receiving adownlink transmission from the access node 106, the relay node 102 wouldattempt to decode the error detection bits. If the decoding issuccessful, the relay node 102 accepts the data packet associated withthe data transmission and sends an acknowledgement (ACK) message to theaccess node 106. If the decoding is unsuccessful, the relay node 102places the data packet associated with the data transmission in a bufferand sends a negative-acknowledgement (NACK) message to the access node106. Hereinafter, an ACK message or a NACK message will be referred toas an ACK/NACK.

When the access node 106 gives an uplink grant to the relay node 102 orwhen the relay node 102 gives an uplink grant to the UA 110, thecomponent receiving the grant typically transmits on the uplink 4 mslater. The component that is transmitted to (i.e., the component thatprovided the grant) typically returns an ACK/NACK to the transmittingcomponent 4 ms after the transmission. Therefore, the typical round triptime from the uplink grant to the ACK/NACK is 8 ms.

MBSFN subframes can have a periodicity of either 10 ms or 40 ms,depending on how often a pattern of MBSFN subframes is repeated. Whenthe same subframes in every radio frame are MBSFN subframes, theperiodicity is 10 ms. For example, if subframes 1 and 7 in every radioframe of a series of radio frames were MBSFN subframes, the MBSFNperiodicity would be 10 ms. Alternatively, the pattern of MBSFNsubframes within a series of radio frames might be repeated every 40 ms.For example, subframes 1 and 7 in a first radio frame might be MBSFNsubframes, subframes 2 and 8 in a second radio frame might be MBSFNsubframes, subframe 3 in a third radio frame might be an MBSFN subframe,and subframe 6 in a fourth radio frame might be an MBSFN subframe. Thispattern of MBSFN subframes might then be repeated starting with a fifthradio frame. In such a case, the MBSFN subframe periodicity would be 40ms.

The relay node 102 can transmit reference signals, ACK/NACKs, and uplinkgrants to the UA 110 in the first few symbols of what would otherwise bea reception subframe for the relay node 102. After transmitting suchinformation, the relay node 102 switches to a receive mode to receivedata from the access node 106.

Several HARQ-related issues might arise involving conflicts among thetransmissions that occur in the access link 108 and the relay link 104.Some issues might be related to the relay node 102 missing atransmission from the access node 106, other issues might be related tothe relay node 102 missing a transmission from the UA 110, and otherissues might be related to the transmission of multiple ACK/NACKS.

If a relay node happens to be scheduled to transmit to a UA on thedownlink 8 ms after the relay node receives an uplink grant from anaccess node, interference will occur between the relay node'stransmission to the UA and the relay node's reception of an ACK/NACKfrom the access node. More specifically, 4 ms after receiving an uplinkgrant, the relay node transmits on the uplink to the access node. 4 msafter the uplink transmission, the access node sends an ACK/NACK to therelay node. If the relay node was already scheduled for transmission tothe UA on the downlink at that time (for example, in subframes 0, 4, 5,9), the relay node would need to receive the ACK/NACK on the downlinkfrom the access node and transmit on the downlink to the UA at the sametime. Since the relay node cannot receive and transmit on the samefrequency band at the same time, the relay node would not receive theACK/NACK from the access node.

This problem is illustrated in FIG. 2, where a timeline of downlinkreceptions by a relay node from an access node and downlinktransmissions from the relay node to a UA is depicted. In this example,subframes 1 and 7 are MBSFN subframes. That is, the relay node canreceive data on a downlink from the access node in subframes 1 and 7.The capability to receive on the downlink in a subframe is denoted bythe letters “RX” in that subframe. In other examples, other subframescould be MBSFN subframes. Also, an MBSFN periodicity of 10 ms is shownin this example. That is, subframes 1 and 7 are MBSFN subframes in everyradio frame. Downlink transmissions from the relay node to the UA mustoccur at subframes 0, 4, 5, and 9, as described above. The requirementto transmit a full subframe on the downlink in a subframe is denoted bythe letters “TX” in that subframe. Other subframes could be also usedfor the downlink transmissions from the relay node to the UA.

In this example, the relay node receives an uplink grant from the accessnode at subframe 1. 4 ms later, at subframe 5, the relay node transmitson the uplink to the access node. (Only a portion of the timeline foruplink transmissions to and from the relay node is shown in the figure.)4 ms after the relay node transmits to the access node, the access nodesends an ACK/NACK to the relay node. That is, the access node sends theACK/NACK at subframe 9. However, a downlink transmission from the relaynode to the UA was already scheduled to occur at subframe 9 (i.e., theMBSFN subframe configuration cannot be in subframe 0, 4, 5, 9 in a radioframe). The relay node cannot receive the ACK/NACK and transmit to theUA at the same time, so the relay node misses the ACK/NACK that theaccess node sends at subframe 9.

In an embodiment, a multi-mode HARQ transmission scheme can be used tosolve the problem of the relay node missing an ACK/NACK from the accessnode. That is, the solution includes two parts, one addressing caseswhere the MBSFN subframe periodicity is 10 ms, and one addressing caseswhere the MBSFN subframe periodicity is 40 ms.

When the MBSFN subframe periodicity is 10 ms, synchronous retransmissionis used. In synchronous retransmission, a component retransmits a datapacket at a specified time after receiving a NACK from another componentto which it transmitted the data packet. In an embodiment, the timing ofHARQ transmissions from the access node to the relay node is modifiedsuch that the access node sends the relay node an ACK/NACK 6 ms after anuplink transmission from the relay node to the access node, rather thanthe standard 4 ms later, while the relay node always transmits the datato the access node 4 ms after the uplink grant is received. In anotherembodiment, the relay node receives the uplink grant in subframe k, andthe relay node transmits the data to the access node in subframe k+mwhile the access node sends the relay node an ACK/NACK in subframe k+10(here m is less than 10). In this way, the round trip time from the timeof the uplink grant to the time of the ACK/NACK is then 10 ms. Changingthe timing of the ACK/NACK in this manner ensures that, when theperiodicity is 10 ms, the access node never sends an ACK/NACK when therelay node is trying to transmit on the downlink. The ACK/NACK is alwayssent 10 ms after the relay node receives an uplink grant, and receivingan uplink grant always occurs in an MBSFN subframe. Since theperiodicity is 10 ms, the subframe that occurs 10 ms after an uplinkgrant will also be an MBSFN subframe, and the ACK/NACK can be receivedin that MBSFN subframe.

An example of this partial solution is illustrated in FIG. 3, whichshows a relay node downlink timeline with the same MBSFN subframepattern and periodicity as that in FIG. 2. The relay node again receivesan uplink grant from the access node at subframe 1 and transmits on theuplink 4 ms later, at subframe 5. (Again, only a portion of the timelinefor relay node uplink transmissions is shown.) In this embodiment, theaccess node sends an ACK/NACK to the relay node 6 ms after the relaynode transmits on the uplink to the access node. That is, since theround trip time is now 10 ms, the access node sends the relay node anACK/NACK 10 ms after providing the uplink grant. This places theACK/NACK at subframe 1 of the next radio frame. Since subframe 1 of thesecond radio frame, like subframe 1 of the first radio frame, is anMBSFN subframe, the relay node can receive the ACK/NACK.

This partial solution may not be appropriate when the periodicity is 40ms. In that case, each radio frame in a set of four consecutive radioframes might have a different pattern of MBSFN subframes. If theACK/NACK from the access node to the relay node is set to always occurin the same subframe of each radio frame, the ACK/NACK might occur in a“receive” subframe in one radio frame, but that subframe might be a“transmit” subframe in one or more of the other three radio frames ofthat set of four. Therefore, the interference problems described abovecould occur.

For example, subframe 1 might be an MBSFN subframe in the first of fourconsecutive radio frames, and the relay node might receive an uplinkgrant in that subframe. If the round trip time is set to 10 ms, asdescribed above, the access node would send the relay node an ACK/NACKat subframe 1 of the next radio frame. However, the next radio framemight have a different MBSFN subframe pattern, and subframe 1 of thatradio frame might be a subframe in which the relay is scheduled totransmit on the downlink. The relay node would not be able to receivethe ACK/NACK and transmit on the downlink at the same time, and theACK/NACK would be missed.

Therefore, in an embodiment, when the MBSFN subframe periodicity is 40ms, asynchronous retransmission is used. In asynchronous retransmission,a component may be instructed to retransmit a data packet at anarbitrary (rather than fixed) time after the original data packettransmission. More specifically, in this portion of the solution in thisembodiment, the access node does not send an ACK/NACK to the relay node.Instead, the access node sends the relay node a grant for an uplinkretransmission when retransmission is required and does not send a grantwhen retransmission is not required. When the relay node receives thegrant for the uplink retransmission, the relay node regards the grant asa request for a retransmission, and it retransmits the missed datapacket in the corresponding scheduled uplink “transmit” subframe. Theproblem of the relay node missing an ACK/NACK is eliminated because theaccess node never sends an ACK/NACK in this case.

A complete solution in this embodiment is therefore to use a multi-modeHARQ transmission, with a different mode for each of the two possibleMBSFN periodicities. When the MBSFN periodicity is 10 ms, synchronousretransmission and a 10 ms round trip time are used. When the MBSFNperiodicity is 40 ms, asynchronous retransmission is used, and theaccess node informs the relay node of the need for a retransmission bysending an uplink grant rather than a NACK. In another embodiment,asynchronous retransmission applies for MBSFN periodicities of both 10ms and 40 ms. That is, regardless of whether a 10 ms periodicity or a 40ms periodicity is used, the access node sends the relay node anasynchronous grant for an uplink retransmission when a data packet ismissed, and when the relay node receives the grant for the uplinkretransmission, the relay node retransmits the missed data packet.

In an alternative embodiment, the problem of the relay node missing anACK/NACK from the access node after sending an uplink transmission tothe access node is addressed in a different manner. In this case, theaccess node does not send an ACK/NACK 4 ms after receiving an uplinktransmission from the relay node, as might be done under currentprocedures. Instead, the access node sends an ACK/NACK to the relay nodein the first MBSFN subframe that is at least 4 ms after the uplinktransmission from the relay node.

For example, if subframes 1 and 7 in a radio frame are MBSFN subframes,and the access node sends the relay node an uplink grant at subframe 1,the relay node will transmit on the uplink to the access node 4 mslater, at subframe 5. The access node will then send an ACK/NACK to therelay node at the next MBSFN subframe that is more than 4 ms later,which would be subframe 1 in the next radio frame. Since the ACK/NACKsare always transmitted in MBSFN subframes, there will be no conflictcaused by the relay node attempting to receive an ACK/NACK in a subframein which the relay node is scheduled to transmit.

It is possible that the relay node could send multiple uplinktransmissions to the access node before the next opportunity for theaccess node to transmit an ACK/NACK to the relay node. The access nodewould need to send an ACK/NACK for each of the uplink transmissions butmay not necessarily be able to send the ACK/NACKs in the same subframe.FIG. 4 illustrates an example where subframes 1 and 2 are MBSFNsubframes in which uplink grants are provided to the relay node. Uplinktransmissions from the relay to the access node then occur 4 ms later atsubframes 5 and 6. The next MBSFN subframe that is at least 4 ms laterthan the uplink transmissions is at subframe 1 of the next radio frame,so the ACK/NACKs for the uplink transmissions that occurred at subframes5 and 6 might, under a preliminary solution, occur at subframe 1. Undercurrent procedures, however, two ACK/NACKs cannot occur in the samesubframe.

Such a situation might be addressed in one of two different ways. In oneembodiment, the ACK/NACK for the second uplink transmission can bedelayed to the next MBSFN subframe that does not already have ascheduled ACK/NACK. This is illustrated in FIG. 5, where the ACK/NACKfor the uplink transmission that occurred at subframe 5 occurs atsubframe 1 of the next radio frame, and the ACK/NACK for the uplinktransmission that occurred at subframe 6 occurs at subframe 7 of thenext radio frame. This embodiment could add delays in the return of theACK/NACKS, but no modifications would be needed to the currentprocedures for ACK/NACK coding.

In an alternative embodiment, multiple ACK/NACKs could be aggregatedinto a single ACK/NACK transmission. This is illustrated in FIG. 6,where both of the ACK/NACKs for the uplink transmissions that occurredat subframes 5 and 6 are aggregated into a single ACK/NACK transmissionthat occurs in subframe 1. This embodiment avoids delays in the returnof the ACK/NACKS but may require changes to the current procedures forACK/NACK coding.

The problem of the relay node missing an ACK/NACK from the access nodeafter sending an uplink transmission to the access node is addressed inyet another manner in another alternative embodiment. In this case, forevery MBSFN subframe in which the access node grants an uplink resourceto the relay node, a corresponding MBSFN subframe is assigned in whichthe relay node can receive an ACK/NACK from the access node for theuplink transmission that the relay node sent to the access node on thegranted resource. The mapping between the uplink grant MBSFN subframesand the ACK/NACK subframes can be explicitly signaled from the accessnode to the relay node during MBSFN configuration, or implicitly definedby certain rules.

FIG. 7 illustrates an example of such a mapping between MBSFN subframes.In this example, MBSFN subframe 2 is designated as a subframe in whichan uplink grant will occur, and subframe 13 is designated as thesubframe in which an ACK/NACK will be returned for the transmission onthe uplink that was granted in subframe 2. Similarly, subframes 13, 22,and 33 are designated as uplink grant subframes, and subframes 22, 33,and 2, respectively, are designated as the corresponding ACK/NACKsubframes. In other examples, other mappings between MBSFN subframes andcorresponding ACK/NACK subframes could be used. The mapping can besemi-static, and the signaling that is used to send the mapping from theaccess node to the relay node can be higher layer signaling such asradio resource control (RRC) signaling or media access control (MAC)control elements.

While the embodiments described above have been presented as separatesolutions for dealing with the problem of the relay node missing anACK/NACK from the access node after sending an uplink transmission tothe access node, it should be understood that these solutions could becombined in various combinations.

Other issues might arise when a relay node transmits to an access nodeat the same time that a UA is attempting to transmit to the relay node.In some cases, the relay node might be sending data on the uplink to theaccess node after receiving an uplink grant from the access node, and inother cases, the relay node might be sending an ACK/NACK on the uplinkto the access node after receiving data on the downlink from the accessnode. In either case, if the UA attempts to transmit to the relay nodein the same subframe in which the relay node is transmitting to theaccess node, the relay node will miss the transmission from the UA.

This can occur because, as mentioned above, the relay node can transmitcontrol information to the UA in the first few symbols of what wouldotherwise be a reception subframe for the relay node. After transmittingthe control information, the relay node can receive data from the accessnode in the remainder of the subframe. If the relay node provides anuplink grant to the UA, the UA will typically transmit to the relay nodein a subframe that occurs 4 ms later. If the relay node receives data oran uplink grant from the access node, the relay node will send anACK/NACK or data to the access node in a subframe that occurs 4 mslater. Therefore, if the relay node receives data or an uplink grantfrom the access node in the same subframe in which the relay nodeprovided an uplink grant to the UA, the relay node will attempt totransmit to the access node in the same subframe in which the UA isattempting to transmit to the relay node. The relay node will miss thetransmission from the UA when such a collision occurs.

In an embodiment, this situation can be addressed by the relay nodesending the UA a “smart” NACK when the relay node knows that it hasmissed a transmission from the UA. The relay node knows that when itprovides an uplink grant to the UA, the UA will transmit to the relaynode 4 ms later. The relay node also knows that when it receives atransmission from the access node, the relay node will transmit to theaccess node 4 ms later. Therefore, the relay node knows that when itprovides an uplink grant to the UA and receives a transmission from theaccess node in the same subframe, a collision will occur 4 ms later andthe relay node will miss a transmission from the UA. In an embodiment,the relay node sends the UA a smart NACK message when the relay nodeknows that it has missed a transmission from the UA for this reason. Thesmart NACK message can be sent 4 ms or four subframes after the inferredcollision. The UA can then retransmit the missed data packet to therelay node 4 ms or four subframes later. The NACK can be referred to as“smart” since it is based on the relay node being aware that atransmission from the UA has been missed due to a collision.

A data packet transmitted from the UA to the relay node typically uses aparticular redundancy version. If the data packet needs to beretransmitted, the retransmission might use a redundancy versiondifferent from that used in the initial transmission. The two packetswith the different redundancy versions might then be combined toincrease the likelihood that the data will be properly decoded. Whenadaptive retransmission is used, the relay node explicitly signals theUA which redundancy version to use for a retransmission. Whennon-adaptive retransmission is used, the redundancy version to be usedfor a retransmission is determined by a periodic cycle of redundancyversions. For example, if a cycle of 0-2-1-3 is used, then redundancyversion 0 would be used on the initial transmission, redundancy version2 would be used on the first retransmission, redundancy version 1 wouldbe used on the second retransmission, and redundancy version 3 would beused on the third retransmission. Redundancy version 0 typicallyincludes more information and better information than the otherredundancy versions for decoding purposes, so redundancy version 0 istypically used on an initial transmission. Additional information aboutredundancy versions can be found in 3rd Generation Partnership Project(3GPP) Technical Specification (TS) 36.212, which is incorporated hereinby reference for all purposes.

When a data packet transmitted from the UA to the relay node is missedfor the reason described above and is later retransmitted, it is knownthat the first data packet was never received and that it thereforecannot be combined with the retransmitted data packet. That is, thereason for the retransmission is not an inability of the relay node todecode the initial data packet, but the fact that the relay node neverreceived the initial data packet at all.

In an embodiment, when the relay node misses a data packet for thereason described above and sends the UA a smart NACK, the UA retransmitsthe data packet using the same redundancy version that was used on theinitial transmission. More specifically, since redundancy version 0 istypically used on an initial transmission and typically provides betterperformance, redundancy version 0 might be used when a UA retransmits adata packet after the UA receives a smart NACK. Alternatively, the UAcould retransmit the data packet using the redundancy version that wasused on the previous transmission. For example, if the UA transmits adata packet using redundancy version 0, but the relay node cannot decodethe packet, the UA might then retransmit using redundancy version 2. Ifthe relay node cannot receive the retransmitted packet (due to an uplinkcollision, for example), the UA would again retransmit with redundancyversion 2. This would provide more diversity after being recombined withthe data packet transmitted with redundancy version 0. Retransmittingwith redundancy version 0 in such a case would provide no parity bitdiversity for HARQ combining.

In an embodiment, when the relay node sends the UA a smart NACK, therelay node might include an indicator that informs the UA that the NACKis a smart NACK. Upon receiving the indicator, the UA knows toretransmit with an appropriate redundancy version. For example, the UAmight be configured to retransmit with either the initial redundancyversion, the previous redundancy version, or redundancy version 0 uponreceiving the indicator. Alternatively, the indicator might explicitlyinstruct the UA to retransmit with either the initial redundancyversion, the previous redundancy version, or redundancy version 0.

These embodiments are illustrated in FIG. 8. At subframe 1, a relay nodereceives a downlink transmission from an access node. In some cases, thedownlink transmission might be an uplink grant from the access node, andin other cases, the downlink transmission might be a downlink datatransmission from the access node. Also in subframe 1, the relay nodeprovides an uplink grant to a UA. 4 ms later, at subframe 5, the UAattempts to transmit on the uplink to the relay node using the uplinkgrant that the relay node provided in subframe 1. Also in subframe 5,the relay node attempts to transmit on the uplink to the access node. Inthe cases where the downlink transmission from the access node to therelay node at subframe 1 was an uplink grant, the transmission from therelay node to the access node at subframe 5 is a data transmission. Inthe cases where the downlink transmission from the access node to therelay node at subframe 1 was a data transmission, the transmission fromthe relay node to the access node at subframe 5 is an ACK/NACK.

The relay node knows that, at subframe 5, the UA is attempting totransmit on the uplink to the relay node at the same time that the relaynode is attempting to transmit on the uplink to the access node and thatthe transmission from the UA will be missed. Therefore, 4 ms after thetransmission from the UA, at subframe 9, the relay node sends a smartNACK on the downlink to the UA informing the UA that the transmission atsubframe 5 was missed. The NACK can be referred to as “smart” since itis based on the relay node being aware of the collision that occurred atsubframe 5. 4 ms after receiving the smart NACK, at subframe 3 of thenext radio frame, the UA retransmits the data that was previouslytransmitted at subframe 5, and the relay node receives theretransmission.

In an alternative embodiment, another technique is used to address theproblem of the relay node missing a transmission from the UA when the UAattempts to transmit to the relay node in the same subframe in which therelay node is transmitting to the access node. In this technique, uplinktransmissions from the relay node to the access node are fixed to occurat regular intervals, such as every 8 ms. Uplink transmissions from theUA to the relay node are then forbidden from occurring at those times.In this way, uplink transmissions from the relay node to the access nodeand uplink transmissions from the UA to the relay node never occur atthe same time.

In order for the uplink transmissions from the relay node to the accessnode to occur at fixed times, modifications might be needed to thetypical 4 ms interval between an uplink grant from the access node andan uplink transmission to the access node. In an embodiment, an uplinkgrant from the access node to the relay node occurs in an MBSFN subframethat is as short a time as possible ahead of a fixed uplink transmissionfrom the relay node, but no less than 4 ms ahead of the fixed uplinktransmission. For example, if a fixed uplink transmission is scheduledto occur in subframe 7, and if an MBSFN subframe occurs at subframe 3,the uplink grant for the fixed uplink transmission occurs in the MBSFNsubframe at subframe 3. If a fixed uplink transmission is scheduled tooccur in subframe 7, and if an MBSFN subframe does not occur at subframe3 but does occur at subframe 2, the uplink grant for the fixed uplinktransmission occurs in the MBSFN subframe at subframe 2, and so on. If afixed uplink transmission is scheduled to occur in subframe 9, and if anMBSFN subframe occurs at subframe 6, 7, or 8, the uplink grant for thefixed uplink transmission does not occur in any of these MBSFNsubframes, since these subframes are less than 4 ms ahead of the fixeduplink transmission.

Also, in order to ensure that uplink transmissions from the UA to therelay node are forbidden in the fixed subframes in which uplinktransmissions from the relay node to the access node occur,modifications might be needed to the procedures by which the relay nodesends data and uplink grants to the UA. More specifically, the relaynode should not send data or an uplink grant to the UA 4 ms before asubframe in which the UA is forbidden from transmitting to the relaynode, since sending data or an uplink grant to the UA in such a subframewill cause the UA to transmit an ACK/NACK or data to the relay node inthe forbidden subframe. In addition, there may be some subframes inwhich the relay node would not transmit data to the UA since thesubframes are MBSFN subframes, but in which the relay can provide anuplink grant to the UA since a subframe in which the UA is forbiddenfrom transmitting to the relay node does not occur 4 ms later.

An example of this embodiment is illustrated in FIG. 9, where a timelinefor downlink receptions by the relay node from the access node anddownlink transmissions from the relay node to the UA is labeled R-DL, atimeline for uplink transmissions from the relay node to the access nodeis labeled R-UL, a timeline for downlink transmissions from the relaynode to the UA is labeled A-DL, and a timeline for uplink transmissionsfrom the UA to the relay node is labeled A-UL.

In this example, the relay node transmits on the uplink to the accessnode at regular 8 ms intervals labeled with the letter C in the R-ULtimeline. To prevent collisions between these fixed relay node uplinktransmissions, the UA is barred from transmitting to the relay node inthese subframes. The subframes in which the UA is barred fromtransmitting are labeled with the letter G in the A-UL timeline. TheUA's uplink HARQ process numbers associated with the subframes are alsoshown in the A-UL timeline. Since the UA cannot transmit in the “G”subframes, the uplink HARQ process in those subframes will not beavailable. In this example, since the “G” subframes are associated withHARQ process 0, HARQ process 0 will be lost. Since the “C” subframes,where the relay node transmits to the access node and where the UA isforbidden from transmitting to the relay node, occur at the same 8 msinterval as one cycle of HARQ processes, the same HARQ process will belost out of every cycle of HARQ processes.

In order for the relay node to transmit on the uplink to the access nodeat the regularly spaced “C” subframes, the subframes in which the uplinkgrants are provided to the relay node for the uplink transmissions mightneed to be specified as described above. The uplink grants occur inMBSFN subframes, which are labeled with the letter B in the R-DLtimeline. Subframes in which the relay node must transmit on thedownlink to the UA are labeled with the letter A in the R-DL timeline.

In the example of FIG. 9, the “C” subframes occur at subframes 0, 8, 16,24, and 32. For the “C” subframe that occurs at subframe 8, the relaynode receives an uplink grant from the access node at subframe 3. Theclosest subframe to subframe 8 that is 4 or more ms ahead of subframe 8is subframe 4. This is an “A” subframe in which downlink transmissionsto the UA must be made, so subframe 4 cannot be an MBSFN subframe. Thenext closest subframe that is 4 ms or more ahead of subframe 8 issubframe 3. That subframe is not an “A” subframe, so that subframe isdesignated as an MBSFN subframe, and an uplink grant for the uplinktransmission at subframe 8 is made in subframe 3.

For the “C” subframe that occurs at subframe 16, the relay node receivesan uplink grant from the access node at subframe 12. Although subframe13 is closer to subframe 16 and is not an “A” subframe in which downlinktransmissions to the UA must be made, subframe 13 could not be used asan MBSFN subframe in this example since that subframe is less than 4 msahead of the “C” subframe at subframe 16.

For the “C” subframe that occurs at subframe 24, the relay node receivesan uplink grant from the access node at subframe 18. The two closestsubframes to subframe 24 that are 4 or more ms ahead of subframe 24 aresubframes 19 and 20. Both of these are “A” subframes in which downlinktransmissions to the UA must be made, so these cannot be MBSFNsubframes. The next closest subframe that is 4 ms or more ahead ofsubframe 24 is subframe 18, so that subframe is designated as an MBSFNsubframe, and an uplink grant for the uplink transmission at subframe 24is made in subframe 18.

For the “C” subframe that occurs at subframe 32, the relay node receivesan uplink grant from the access node at subframe 28 since that is thesubframe that is as short a time as possible ahead of the “C” subframe,but is not less than 4 ms ahead of the “C” subframe and is not an “A”subframe.

Similarly, for the “C” subframe that occurs at subframe 0, the relaynode receives an uplink grant from the access node at subframe 36 of theprevious set of four radio frames, since that subframe is 4 ms ahead ofthe “C” subframe and is not an “A” subframe.

The “G” subframes in the A-UL timeline, where the UA is forbidden fromtransmitting to the relay node, are arranged to coincide with the “C”subframes in the R-UL timeline, where the relay node transmits to theaccess node. In order to ensure that no transmissions occur from the UAto the relay node in these “G” subframes, the downlink transmissionsfrom the relay node to the UA, as shown in the A-DL timeline, may needto be arranged appropriately. A downlink data transmission from therelay node to the UA cannot occur in an MBSFN subframe since the relaynode receives transmissions from the access node in MBSFN subframes, andthe relay node cannot receive transmissions from the access node in thesame subframe in which the relay node transmits data to the UA.

The subframes labeled D and F in the A-DL timeline coincide with MBSFNsubframes, so data cannot be transmitted on the downlink from the relaynode to the UA in the “D” and “F” subframes. The “F” subframes occur 4ms before a “G” subframe in the A-UL timeline, so uplink grants shouldnot be transmitted on the downlink from the relay node to the UA in the“F” subframes in order to prevent the UA from transmitting data on agranted uplink in a “G” subframe. That is, neither data nor uplinkgrants should be sent from the relay node to the UA in an “F” subframe.However, “D” subframes do not occur 4 ms before a “G” subframe, souplink grants may be transmitted from the relay node to the UA in the“D” subframes since data that is transmitted on the granted uplink willnot coincide with an uplink transmission from the relay node to theaccess node.

The “E” subframes in the A-DL timeline are subframes that are not MBSFNsubframes but that occur 4 ms before a “G” subframe in the A-ULtimeline. Neither data nor uplink grants should be sent from the relaynode to the UA in an “E” subframe since a data transmission would causean ACK/NACK to be sent in a “G” subframe, and an uplink grant wouldcause a data transmission to be sent in a “G” subframe.

In other embodiments, subframes other than 8, 16, 24, 32, and so oncould be designated for relay node uplink transmissions to the accessnode, as long as the subframes maintain a regular 8 ms interval. In sucha case, a different uplink HARQ process would be lost. For example,subframes 5, 13, 21, 29, and so on could be reserved for relay nodetransmissions to the access node, and UA transmissions to the relay nodecould be forbidden in those subframes. It can be seen from FIG. 9 thatHARQ process 5 would be lost in such a case.

In an embodiment, a plurality of sets of subframes could be designatedfor relay node uplink transmissions to the access node, where a regular8 ms interval is maintained between the subframes in each set. Forexample, subframes 8, 16, 24, 32, and so on could be reserved for relaynode transmissions to the access node, and subframes 5, 13, 21, 29, andso on could also be reserved for relay node transmissions to the accessnode. UA transmissions to the relay node could be forbidden in all ofthose subframes. This embodiment would provide more opportunities forthe relay node to transmit to the access node without collisions, but aplurality of HARQ processes would be lost out of every HARQ cycle. Inthis example, HARQ processes 0 and 5 would be unavailable.

The access node might send multiple transmissions of data on thedownlink to the relay node before the next opportunity for the relaynode to transmit corresponding ACK/NACKs for the data transmissions tothe access node. The relay node might need to send the access node anACK/NACK for each of the downlink transmissions, but it may not beefficient for the relay node to transmit the ACK/NACKs separately. In anembodiment, the relay node might aggregate the ACK/NACKs and send themto the relay node in a single subframe. The access node might need toinform the relay node how to perform the aggregation and, in alternativeembodiments, there are two different ways in which the access node coulddo so.

In one embodiment, the access node explicitly tells the relay node whichdownlink transmissions to the relay node can have their ACK/NACKsaggregated and which subframe the relay node should use to send theaggregated ACK/NACK to the access node. For example, as shown in FIG.10, the relay node might receive data from the access node in subframes1, 2, and 3. The access node might explicitly or implicitly (forexample, by some pre-defined rules) inform the relay node that theACK/NACKs for the data transmitted in these subframes are to beaggregated together. The access node might also explicitly or implicitly(for example, by some pre-defined rules) inform the relay node of thesubframe in which the aggregated ACK/NACK is to be returned to theaccess node. In this example, the access node has specified that theaggregated ACK/NACK is to be returned in subframe 7. In other examples,the access node might specify that the ACK/NACKs for data transmitted inother subframes should be aggregated and might specify another subframeas the subframe in which the aggregated ACK/NACK is to be returned. Theaccess node might also explicitly or implicitly (for example, by somepre-defined rules) inform the relay node of the resources used totransmit the aggregated ACK/NACKs.

In an alternative embodiment, the access node includes a one-bitindicator with each downlink transmission to the relay node. Theindicator indicates whether the ACK/NACK for that downlink transmissioncan be aggregated or should be transmitted the usual 4 ms after thedownlink transmission. For example, one value for the indicator couldindicate “do not transmit 4 ms later”. That is, this value couldindicate that the ACK/NACK for a downlink transmission in which theindicator is included should be held for aggregation with laterACK/NACKs. Another value for the indicator could indicate “transmit 4 mslater”. That is, this value could indicate that the ACK/NACK for adownlink transmission in which the indicator is included and any otherprevious ACK/NACKs that have been aggregated should be transmitted 4 msafter the downlink transmission is received.

In this embodiment, if the relay node misses an indicator, theaggregated ACK/NACKs could lose their synchronization. For example, if a“transmit 4 ms later” indicator is missed, the relay will wait for thenext “transmit 4 ms later” indicator to transmit ACK/NACKs, but theaccess node will try to decode what it assumes are ACK/NACKs that shouldhave been sent after the first “transmit 4 ms later” indicator. Toremedy this situation, if the access node can detect that its attemptsat decoding ACK/NACKs are out of synchronization with the relay node'stransmissions of ACK/NACKs, the access node can recover by sendingmultiple “transmit 4 ms later” indicators. Alternatively, this situationmight be avoided if the eNB periodically sends “transmit 4 ms later”indicators.

In either technique by which the access node informs the relay nodeabout how to perform aggregation, aggregated ACK/NACKs can betransmitted in the same subframe as regular uplink data. In cases whereMultiple Input Multiple Output (MIMO) is used, each transmission canconsist of two code words, and the multiplexing of the aggregatedACK/NACKs with the code words of regular data can be done in severaldifferent ways. For example, a first ACK/NACK for subframe 1 could bemultiplexed with code word 1 of a regular data transmission from therelay node to the access node, and then a second ACK/NACK for subframe 1could be multiplexed with code word 2. This pattern could then berepeated for the ACK/NACKs for subframes 2 and 3. In another example, afirst ACK/NACK for subframe 1, a first ACK/NACK for subframe 2, and afirst ACK/NACK for subframe 3 could be multiplexed with code word 1 of aregular data transmission. This pattern could then be repeated for codeword 2. Other multiplexing methods may be apparent to one of skill inthe art.

The UA 110, the relay node 102, the access node 106, and othercomponents described above might include a processing component that iscapable of executing instructions related to the actions describedabove. FIG. 11 illustrates an example of a system 1300 that includes aprocessing component 1310 suitable for implementing one or moreembodiments disclosed herein. In addition to the processor 1310 (whichmay be referred to as a central processor unit or CPU), the system 1300might include network connectivity devices 1320, random access memory(RAM) 1330, read only memory (ROM) 1340, secondary storage 1350, andinput/output (I/O) devices 1360. These components might communicate withone another via a bus 1370. In some cases, some of these components maynot be present or may be combined in various combinations with oneanother or with other components not shown. These components might belocated in a single physical entity or in more than one physical entity.Any actions described herein as being taken by the processor 1310 mightbe taken by the processor 1310 alone or by the processor 1310 inconjunction with one or more components shown or not shown in thedrawing, such as a digital signal processor (DSP) 1380. Although the DSP1380 is shown as a separate component, the DSP 1380 might beincorporated into the processor 1310.

The processor 1310 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 1320,RAM 1330, ROM 1340, or secondary storage 1350 (which might includevarious disk-based systems such as hard disk, floppy disk, or opticaldisk). While only one CPU 1310 is shown, multiple processors may bepresent. Thus, while instructions may be discussed as being executed bya processor, the instructions may be executed simultaneously, serially,or otherwise by one or multiple processors. The processor 1310 may beimplemented as one or more CPU chips.

The network connectivity devices 1320 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 1320 may enable the processor 1310 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 1310 might receiveinformation or to which the processor 1310 might output information. Thenetwork connectivity devices 1320 might also include one or moretransceiver components 1325 capable of transmitting and/or receivingdata wirelessly.

The RAM 1330 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 1310. The ROM 1340 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 1350. ROM 1340 mightbe used to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 1330 and ROM 1340 istypically faster than to secondary storage 1350. The secondary storage1350 is typically comprised of one or more disk drives or tape drivesand might be used for non-volatile storage of data or as an over-flowdata storage device if RAM 1330 is not large enough to hold all workingdata. Secondary storage 1350 may be used to store programs that areloaded into RAM 1330 when such programs are selected for execution.

The I/O devices 1360 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 1325 might be considered to be a component of the I/Odevices 1360 instead of or in addition to being a component of thenetwork connectivity devices 1320.

In an embodiment, a method is provided for preventing a relay node frommissing a transmission from an access node. The method includes, when aten millisecond periodicity is used for Multicast/Broadcast SingleFrequency Network (MBSFN) subframes, setting a time between an uplinkgrant from the access node to the relay node and anacknowledgement/negative-acknowledgement message (ACK/NACK) from theaccess node to the relay node equal to ten milliseconds. The methodfurther includes, when a forty millisecond periodicity is used for MBSFNsubframes, the access node sending the relay node an asynchronous grantfor an uplink retransmission when a data packet is missed, and when therelay node receives the grant for the uplink retransmission, the relaynode retransmitting the missed data packet.

In another embodiment, an access node in a wireless telecommunicationssystem is provided. The access node includes a processor configured,when a ten millisecond periodicity is used for Multicast/BroadcastSingle Frequency Network (MBSFN) subframes, to set a time between anuplink grant from the access node to a relay node and anacknowledgement/negative-acknowledgement message (ACK/NACK) from theaccess node to the relay node equal to ten milliseconds. The processoris further configured, when a forty millisecond periodicity is used forMBSFN subframes, to send the relay node a grant for an uplinkretransmission when a data packet is missed.

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured, whena ten millisecond periodicity is used for Multicast/Broadcast SingleFrequency Network (MBSFN) subframes, to receive anacknowledgement/negative-acknowledgement message (ACK/NACK) from anaccess node. The time between an uplink grant from the access node tothe relay node and the ACK/NACK from the access node to the relay nodeis set equal to ten milliseconds. The processor is further configured,when a forty millisecond periodicity is used for MBSFN subframes, toreceive from the access node an asynchronous grant for an uplinkretransmission when a data packet is missed. The processor is furtherconfigured to retransmit the missed data packet when the relay nodereceives the grant for the uplink retransmission.

In another embodiment, a method is provided for preventing a relay nodefrom missing a transmission from an access node. The method includes theaccess node sending an acknowledgement/negative-acknowledgement message(ACK/NACK) to the relay node in the first available Multicast/BroadcastSingle Frequency Network (MBSFN) subframe that is at least fourmilliseconds after an uplink transmission from the relay node.

In another embodiment, an access node in a wireless telecommunicationssystem is provided. The access node includes a processor configured tosend an acknowledgement/negative-acknowledgement message (ACK/NACK) to arelay node in the first available Multicast/Broadcast Single FrequencyNetwork (MBSFN) subframe that is at least four milliseconds after anuplink transmission from the relay node.

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured toreceive an acknowledgement/negative-acknowledgement message (ACK/NACK)from an access node in the first available Multicast/Broadcast SingleFrequency Network (MBSFN) subframe that is at least four millisecondsafter an uplink transmission from the relay node.

In another embodiment, a method is provided for preventing a relay nodefrom missing a transmission from an access node. The method includes,for every Multicast/Broadcast Single Frequency Network (MBSFN) subframein which the access node grants an uplink resource to the relay node,assigning a corresponding MBSFN subframe in which the access node cantransmit an acknowledgement/negative-acknowledgement message (ACK/NACK)to the relay node for an uplink transmission that the relay node sent tothe access node on the granted resource.

In another embodiment, an access node in a wireless telecommunicationssystem is provided. The access node includes a processor configured totransmit an acknowledgement/negative-acknowledgement message (ACK/NACK)to a relay node for an uplink transmission that the relay node sent tothe access node, wherein, for every Multicast/Broadcast Single FrequencyNetwork (MBSFN) subframe in which the access node grants an uplinkresource to the relay node, a corresponding MBSFN subframe has beenassigned in which the access node can transmit the ACK/NACK.

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured toreceive an acknowledgement/negative-acknowledgement message (ACK/NACK)from an access node for an uplink transmission that the relay node sentto the access node, wherein, for every Multicast/Broadcast SingleFrequency Network (MBSFN) subframe in which the access node grants anuplink resource to the relay node, a corresponding MBSFN subframe hasbeen assigned in which the access node can transmit the ACK/NACK.

In another embodiment, a method is provided for preventing a relay nodefrom missing a transmission from a user agent (UA). The method includes,when the UA transmits a data packet to the relay node in the samesubframe in which the relay node is transmitting to an access node, therelay node sending the UA a negative-acknowledgement message (NACK).

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured tosend a negative-acknowledgement message (NACK) to a user agent (UA) whenthe UA transmits a data packet to the relay node in the same subframe inwhich the relay node is transmitting to an access node.

In another embodiment, a user agent (UA) is provided. The UA includes aprocessor configured to receive a negative-acknowledgement message(NACK) from a relay node when the UA transmits a data packet to therelay node in the same subframe in which the relay node is transmittingto an access node.

In another embodiment, a method is provided for preventing a relay nodefrom missing a transmission from a user agent (UA). The method includestransmitting from the relay node to an access node only at fixedintervals. The method further includes forbidding transmissions from theUA to the relay node during subframes in which the fixed transmissionsfrom the relay node to the access node occur.

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured totransmit to an access node only at fixed intervals, whereintransmissions from a user agent (UA) to the relay node are forbiddenduring subframes in which the fixed transmissions from the relay node tothe access node occur.

In another embodiment, an access node in a wireless telecommunicationssystem is provided. The access node includes a processor configured toreceive transmissions from a relay node, wherein the transmissions occuronly at fixed intervals, and wherein transmissions from a user agent(UA) to the relay node are forbidden during subframes in which the fixedtransmissions from the relay node to the access node occur.

In another embodiment, a method is provided for managing a plurality ofacknowledgement/negative-acknowledgement messages (ACK/NACKs). Themethod includes, when an access node sends multiple transmissions ofdata to a relay node before the next opportunity for the relay node totransmit corresponding ACK/NACKs for the data transmissions to theaccess node, the relay node aggregating the ACK/NACKs and sending theaggregated ACK/NACKs to the access node in a single subframe.

In another embodiment, a relay node in a wireless telecommunicationssystem is provided. The relay node includes a processor configured toaggregate a plurality of acknowledgement/negative-acknowledgementmessages (ACK/NACKs) when an access node sends multiple transmissions ofdata to the relay node before the next opportunity for the relay node totransmit corresponding ACK/NACKs for the data transmissions to theaccess node. The processor is further configured to send the aggregatedACK/NACKs to the access node in a single subframe.

In another embodiment, an access node in a wireless telecommunicationssystem is provided. The access node includes a processor configured toreceive an aggregated acknowledgement/negative-acknowledgement message(ACK/NACK) in a single subframe from a relay node, the aggregatedACK/NACK being formed from a plurality of ACK/NACKs when the access nodesends multiple transmissions of data to the relay node before the nextopportunity for the relay node to transmit corresponding ACK/NACKs forthe data transmissions to the access node.

The following is incorporated herein by reference for all purposes: 3rdGeneration Partnership Project (3GPP) Technical Specification (TS)36.212. Appendices A and B which are attached hereto are alsoincorporated by reference.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the scopeof the present disclosure. The present examples are to be considered asillustrative and not restrictive, and the intention is not to be limitedto the details given herein. For example, the various elements orcomponents may be combined or integrated in another system or certainfeatures may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. A method for preventing a first network node from missing atransmission from a second network node, comprising: when a tenmillisecond periodicity is used for Multicast/Broadcast Single FrequencyNetwork (MBSFN) subframes, setting a time between an uplink grant fromthe second network node to the first network node and anacknowledgement/negative-acknowledgement message (ACK/NACK) from thesecond network node to the first network node equal to ten milliseconds;and when a forty millisecond periodicity is used for MBSFN subframes,the second network node sending the first network node an asynchronousgrant for an uplink retransmission when a data packet is missed, andwhen the first network node receives the grant for the uplinkretransmission, the first network node retransmitting the missed datapacket.
 2. The method of claim 1, wherein the transmission that ismissed is an ACK/NACK that otherwise would have been sent eightmilliseconds after the uplink grant.
 3. The method of claim 2, whereinthe ACK/NACK is missed because the first network node was scheduled totransmit to one or more user agents at the same time that the secondnetwork node attempted to send the ACK/NACK to the first network node.4. The method of claim 1, wherein the time between the uplink grant fromthe second network node to the first network node and the ACK/NACKcomprises four milliseconds from the time of the uplink grant to a timeof an uplink transmission from the first network node to the secondnetwork node and six milliseconds from the time of the uplinktransmission from the first network node to the second network node andthe time of the ACK/NACK.
 5. The method of claim 1, wherein the firstnetwork node is one of: a relay node, an access node, an E-node B, awireless access point, a layer one relay node, a layer two relay node, alayer 3 relay node, a pico-cell, or a femto-cell, and wherein the secondnetwork node is one of: a relay node, an access node, an E-node B, awireless access point, a layer one relay node, a layer two relay node, alayer 3 relay node, a pico-cell, or a femto-cell.
 6. A first networknode in a wireless telecommunications system, comprising: a processorconfigured, when a ten millisecond periodicity is used forMulticast/Broadcast Single Frequency Network (MBSFN) subframes, to set atime between an uplink grant from the first network node to a secondnetwork node and an acknowledgement/negative-acknowledgement message(ACK/NACK) from the first network node to the second network node equalto ten milliseconds, and the processor further configured, when a fortymillisecond periodicity is used for MBSFN subframes, to send the secondnetwork node a grant for an uplink retransmission when a data packet ismissed.
 7. The first network node of claim 6, wherein the time betweenthe uplink grant from the first network node to the second network nodeand the ACK/NACK comprises four milliseconds from the time of the uplinkgrant to a time of an uplink transmission from the second network nodeto the first network node and six milliseconds from the time of theuplink transmission from the second network node to the first networknode and the time of the ACK/NACK.
 8. The first network node of claim 6,wherein the first network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell, andwherein the second network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell.
 9. Afirst network node in a wireless telecommunications system, comprising:a processor configured, when a ten millisecond periodicity is used forMulticast/Broadcast Single Frequency Network (MBSFN) subframes, toreceive an acknowledgement/negative-acknowledgement message (ACK/NACK)from a second network node, a time between an uplink grant from thesecond network node to the first network node and the ACK/NACK from thesecond network node to the first network node being set equal to tenmilliseconds, the processor further configured, when a forty millisecondperiodicity is used for MBSFN subframes, to receive from the secondnetwork node an asynchronous grant for an uplink retransmission when adata packet is missed, and the processor further configured toretransmit the missed data packet when the first network node receivesthe grant for the uplink retransmission.
 10. The first network node ofclaim 9, wherein the ACK/NACK would otherwise be missed because thefirst network node was scheduled to transmit to one or more user agentsat the same time that the second network node attempted to send theACK/NACK to the first network node.
 11. The first network node of claim9, wherein the first network node is one of: a relay node, an accessnode, an E-node B, a wireless access point, a layer one relay node, alayer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell, and wherein the second network node is one of: a relay node,an access node, an E-node B, a wireless access point, a layer one relaynode, a layer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell.
 12. A first network node in a wireless telecommunicationssystem, comprising: a processor configured to send anacknowledgement/negative-acknowledgement message (ACK/NACK) to a secondnetwork node in the first available Multicast/Broadcast Single FrequencyNetwork (MBSFN) subframe that is at least four milliseconds after anuplink transmission from the second network node.
 13. The first networknode of claim 12, wherein the ACK/NACK would otherwise be missed becausethe second network node was scheduled to transmit to one or more useragents at the same time that the first network node attempted to sendthe ACK/NACK to the second network node.
 14. The first network node ofclaim 12, wherein, when the second network node sends a plurality ofuplink transmissions to the first network node before the nextopportunity for the first network node to transmit an ACK/NACK to thesecond network node, an ACK/NACK for the first of the plurality ofuplink transmissions is placed in the first available MBSFN subframethat is at least four milliseconds after the corresponding uplinktransmission from the second network node, and an ACK/NACK for thesecond of the plurality of uplink transmissions is placed in the nextavailable MBSFN subframe.
 15. The first network node of claim 12,wherein the first network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell, andwherein the second network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell. 16.A first network node in a wireless telecommunications system,comprising: a processor configured to receive anacknowledgement/negative-acknowledgement message (ACK/NACK) from asecond network node in the first available Multicast/Broadcast SingleFrequency Network (MBSFN) subframe that is at least four millisecondsafter an uplink transmission from the first network node.
 17. The firstnetwork node of claim 16, wherein, when the first network node sends aplurality of uplink transmissions to the second network node before thenext opportunity for the second network node to transmit an ACK/NACK tothe first network node, an ACK/NACK for the first of the plurality ofuplink transmissions is placed in the first available MBSFN subframethat is at least four milliseconds after the corresponding uplinktransmission from the first network node, and an ACK/NACK for the secondof the plurality of uplink transmissions is placed in the next availableMBSFN subframe.
 18. The first network node of claim 16, wherein, whenthe first network node sends a plurality of uplink transmissions to thesecond network node before the next opportunity for the second networknode to transmit an ACK/NACK to the first network node, a plurality ofACK/NACKs for the plurality of uplink transmissions are aggregated intoa single ACK/NACK transmission that is sent to the first network node inthe first available MBSFN subframe that is at least four millisecondsafter the last of the plurality of uplink transmissions from the firstnetwork node.
 19. The first network node of claim 16, wherein the firstnetwork node is one of: a relay node, an access node, an E-node B, awireless access point, a layer one relay node, a layer two relay node, alayer 3 relay node, a pico-cell, or a femto-cell, and wherein the secondnetwork node is one of: a relay node, an access node, an E-node B, awireless access point, a layer one relay node, a layer two relay node, alayer 3 relay node, a pico-cell, or a femto-cell.
 20. A first networknode in a wireless telecommunications system, comprising: a processorconfigured to transmit an acknowledgement/negative-acknowledgementmessage (ACK/NACK) to a second network node for an uplink transmissionthat the second network node sent to the first network node, wherein,for every Multicast/Broadcast Single Frequency Network (MBSFN) subframein which the first network node grants an uplink resource to the secondnetwork node, a corresponding MBSFN subframe has been assigned in whichthe first network node can transmit the ACK/NACK.
 21. The first networknode of claim 20, wherein the ACK/NACK would otherwise be missed becausethe second network node was scheduled to transmit to one or more useragents at the same time that the first network node attempted to sendthe ACK/NACK to the second network node.
 22. The first network node ofclaim 20, wherein a mapping between the uplink grant MBSFN subframes andthe ACK/NACK subframes is explicitly signaled from the first networknode to the second network node during MBSFN configuration.
 23. Thefirst network node of claim 20, wherein the first network node is oneof: a relay node, an access node, an E-node B, a wireless access point,a layer one relay node, a layer two relay node, a layer 3 relay node, apico-cell, or a femto-cell, and wherein the second network node is oneof: a relay node, an access node, an E-node B, a wireless access point,a layer one relay node, a layer two relay node, a layer 3 relay node, apico-cell, or a femto-cell.
 24. A first network node in a wirelesstelecommunications system, comprising: a processor configured to receivean acknowledgement/negative-acknowledgement message (ACK/NACK) from asecond network node for an uplink transmission that the first networknode sent to the second network node, wherein, for everyMulticast/Broadcast Single Frequency Network (MBSFN) subframe in whichthe second network node grants an uplink resource to the first networknode, a corresponding MBSFN subframe has been assigned in which thesecond network node can transmit the ACK/NACK.
 25. The first networknode of claim 24, wherein the ACK/NACK would otherwise be missed becausethe first network node was scheduled to transmit to one or more useragents at the same time that the second network node attempted to sendthe ACK/NACK to the first network node.
 26. The first network node ofclaim 24, wherein the mapping is signaled in high-layer signaling thatcomprises at least one of: radio resource control signaling; and mediaaccess control elements.
 27. The first network node of claim 24, whereinthe first network node is one of: a relay node, an access node, anE-node B, a wireless access point, a layer one relay node, a layer tworelay node, a layer 3 relay node, a pico-cell, or a femto-cell, andwherein the second network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell. 28.A first network node in a wireless telecommunications system,comprising: a processor configured to send a negative-acknowledgementmessage (NACK) to a user agent (UA) when the UA transmits a data packetto the first network node in the same subframe in which the firstnetwork node is transmitting to a second network node.
 29. The firstnetwork node of claim 28, wherein the first network node sends the NACKeight subframes after a subframe in which the first network nodeprovided an uplink grant to the UA and in which the first network nodereceived a transmission from the second network node.
 30. The firstnetwork node of claim 28, wherein, when the first network node sends theNACK to the UA, the first network node includes an indicator thatinforms the UA that the NACK is a “smart” NACK.
 31. The first networknode of claim 30, wherein the UA is configured, upon receiving theindicator, to retransmit the data packet using one of: the redundancyversion with which the data packet was initially transmitted; theredundancy version with which the data packet was previouslytransmitted; and redundancy version
 0. 32. The first network node ofclaim 28, wherein the first network node is one of: a relay node, anaccess node, an E-node B, a wireless access point, a layer one relaynode, a layer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell, and wherein the second network node is one of: a relay node,an access node, an E-node B, a wireless access point, a layer one relaynode, a layer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell.
 33. A user agent (UA), comprising: a processor configured toreceive a negative-acknowledgement message (NACK) from a first networknode when the UA transmits a data packet to the first network node inthe same subframe in which the first network node is transmitting to asecond network node.
 34. The UA of claim 33, wherein the first networknode sends the NACK eight subframes after a subframe in which the firstnetwork node provided an uplink grant to the UA and in which the firstnetwork node received a transmission from the second network node. 35.The UA of claim 33, wherein, when the first network node sends the NACKto the UA, the first network node includes an indicator that informs theUA to retransmit the data packet using one of: the redundancy versionwith which the data packet was initially transmitted; the redundancyversion with which the data packet was previously transmitted; andredundancy version
 0. 36. The UA of claim 33, wherein the first networknode is one of: a relay node, an access node, an E-node B, a wirelessaccess point, a layer one relay node, a layer two relay node, a layer 3relay node, a pico-cell, or a femto-cell, and wherein the second networknode is one of: a relay node, an access node, an E-node B, a wirelessaccess point, a layer one relay node, a layer two relay node, a layer 3relay node, a pico-cell, or a femto-cell.
 37. A first network node in awireless telecommunications system, comprising: a processor configuredto transmit to a second network node only at fixed intervals, whereintransmissions from a user agent (UA) to the first network node areforbidden during subframes in which the fixed transmissions from thefirst network node to the second network node occur.
 38. The firstnetwork node of claim 37, wherein the first network node is forbiddenfrom transmitting data to the UA in an MBSFN subframe, but the firstnetwork node is allowed to provide an uplink grant to the UA in theMBSFN subframe if the MBSFN subframe does not occur four millisecondsahead of a subframe in which the UA is forbidden from transmitting tothe first network node.
 39. The first network node of claim 37, whereina plurality of sets of subframes are designated for periodictransmissions from the first network node to the second network node,and wherein an eight millisecond interval is maintained between thesubframes in each set, and wherein transmissions from the UA to thefirst network node are forbidden during the subframes in which theperiodic transmissions occur.
 40. The first network node of claim 37,wherein the first network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell, andwherein the second network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell. 41.A first network node in a wireless telecommunications system,comprising: a processor configured to receive transmissions from asecond network node, wherein the transmissions occur only at fixedintervals, and wherein transmissions from a user agent (UA) to thesecond network node are forbidden during subframes in which the fixedtransmissions from the second network node to the first network nodeoccur.
 42. The first network node of claim 41, wherein the fixedinterval is eight milliseconds.
 43. The first network node of claim 41,wherein an uplink grant for the fixed uplink transmission occurs in aMulticast/Broadcast Single Frequency Network (MBSFN) subframe that isthe closest MBSFN subframe ahead of the uplink grant that is not lessthan four milliseconds ahead of the fixed uplink transmission.
 44. Thefirst network node of claim 41, wherein the transmissions from the UA tothe second network node are forbidden to occur by ensuring that secondnetwork node does not transmit to the UA four milliseconds before asubframe in which the UA is forbidden from transmitting to the secondnetwork node.
 45. The first network node of claim 41, wherein aplurality of sets of subframes are designated for periodic transmissionsfrom the second network node to the first network node, and wherein aneight millisecond interval is maintained between the subframes in eachset, and wherein transmissions from the UA to the second network nodeare forbidden during the subframes in which the periodic transmissionsoccur.
 46. The first network node of claim 31, wherein the first networknode is one of: a relay node, an access node, an E-node B, a wirelessaccess point, a layer one relay node, a layer two relay node, a layer 3relay node, a pico-cell, or a femto-cell, and wherein the second networknode is one of: a relay node, an access node, an E-node B, a wirelessaccess point, a layer one relay node, a layer two relay node, a layer 3relay node, a pico-cell, or a femto-cell.
 47. A first network node in awireless telecommunications system, comprising: a processor configuredto aggregate a plurality of acknowledgement/negative-acknowledgementmessages (ACK/NACKs) when a second network node sends multipletransmissions of data to the first network node before the nextopportunity for the first network node to transmit correspondingACK/NACKs for the data transmissions to the second network node, theprocessor further configured to send the aggregated ACK/NACKs to thesecond network node in a single subframe.
 48. The first network node ofclaim 47 wherein the second network node explicitly informs the firstnetwork node which downlink transmissions to the first network node areallowed to have the ACK/NACKs for the downlink transmissions aggregatedand explicitly informs the first network node which subframe the firstnetwork node is to use to transmit the aggregated ACK/NACK to the secondnetwork node.
 49. The first network node of claim 47, wherein the secondnetwork node includes an indicator with each downlink transmission tothe first network node, the indicator indicating whether the ACK/NACKfor that downlink transmission can be aggregated.
 50. The first networknode of claim 49, wherein, when the indicator indicates that theACK/NACK can be aggregated, the ACK/NACK is held for later transmission,and when the indicator indicates that the ACK/NACK cannot be aggregated,the ACK/NACK and any held ACK/NACKS are transmitted to the secondnetwork node.
 51. The first network node of claim 50, wherein, when thesecond network node detects that its attempts at decoding the ACK/NACKsare out of synchronization with the first network node's transmissionsof the ACK/NACKs, the second network node sends a plurality ofindicators to the first network node indicating that any held ACK/NACKSare to be transmitted to the second network node.
 52. The first networknode of claim 47, wherein the aggregated ACK/NACKs are transmitted inthe same subframe as other uplink data.
 53. The first network node ofclaim 47, wherein the first network node is one of: a relay node, anaccess node, an E-node B, a wireless access point, a layer one relaynode, a layer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell, and wherein the second network node is one of: a relay node,an access node, an E-node B, a wireless access point, a layer one relaynode, a layer two relay node, a layer 3 relay node, a pico-cell, or afemto-cell.
 54. A first network node in a wireless telecommunicationssystem, comprising: a processor configured to receive an aggregatedacknowledgement/negative-acknowledgement message (ACK/NACK) in a singlesubframe from a second network node, the aggregated ACK/NACK beingformed from a plurality of ACK/NACKs when the first network node sendsmultiple transmissions of data to the second network node before thenext opportunity for the second network node to transmit correspondingACK/NACKs for the data transmissions to the first network node.
 55. Thefirst network node of claim 54, wherein the first network nodeexplicitly informs the second network node which downlink transmissionsto the second network node are allowed to have the ACK/NACKs for thedownlink transmissions aggregated and explicitly informs the secondnetwork node which subframe the second network node is to use totransmit the aggregated ACK/NACK to the first network node.
 56. Thefirst network node of claim 54, wherein the first network node includesan indicator with each downlink transmission to the second network node,the indicator indicating whether the ACK/NACK for that downlinktransmission can be aggregated.
 57. The first network node of claim 54,wherein the first network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell, andwherein the second network node is one of: a relay node, an access node,an E-node B, a wireless access point, a layer one relay node, a layertwo relay node, a layer 3 relay node, a pico-cell, or a femto-cell.